On Fri, Oct 11, 2019 at 9:24 PM Borislav Petkov <bp@xxxxxxxxx> wrote: > > On Fri, Sep 20, 2019 at 12:05:21AM +0800, Kairui Song wrote: > > Currently, kernel fails to boot on some HyperV VMs when using EFI. > > And it's a potential issue on all platforms. > > > > It's caused a broken kernel relocation on EFI systems, when below three > > conditions are met: > > > > 1. Kernel image is not loaded to the default address (LOAD_PHYSICAL_ADDR) > > by the loader. > > 2. There isn't enough room to contain the kernel, starting from the > > default load address (eg. something else occupied part the region). > > 3. In the memmap provided by EFI firmware, there is a memory region > > starts below LOAD_PHYSICAL_ADDR, and suitable for containing the > > kernel. > > > > Efi stub will perform a kernel relocation when condition 1 is met. But > > due to condition 2, efi stub can't relocate kernel to the preferred > > address, so it fallback to query and alloc from EFI firmware for lowest > > usable memory region. > > > > It's incorrect to use the lowest memory address. In later stage, kernel > > will assume LOAD_PHYSICAL_ADDR as the minimal acceptable relocate address, > > but efi stub will end up relocating kernel below it. > > So far, so good. > > > Then before the kernel decompressing. Kernel will do another relocation > > to address not lower than LOAD_PHYSICAL_ADDR, this time the relocate will > > over write the blockage at the default load address, which efi stub tried > > to avoid, and lead to unexpected behavior. Beside, the memory region it > > writes to is not allocated from EFI firmware, which is also wrong. > > This paragraph is an unreadable mess and should be rewritten in simple, > declarative sentences. > > The patch itself looks ok. Thanks. I've sent V3 updating that paragraph. > > -- > Regards/Gruss, > Boris. > > https://people.kernel.org/tglx/notes-about-netiquette -- Best Regards, Kairui Song
